1. Field of the Invention
The present invention relates generally to a liquid crystal display device wherein a liquid crystal layer is held between a pair of electrode substrates, and more particularly to a liquid crystal display device whose liquid crystal layer is divided into a plurality of domains among which liquid crystal molecules are set in different tilt directions.
2. Description of the Related Art
Liquid crystal display (LCD) panels are applied to various technical fields of OA equipment, information terminals, watches, televisions, etc., because of their characteristics of lightness, thinness, and low power consumption. In particular, an active matrix type LCD panel has an excellent response characteristic obtained by thin film transistors for switching pixels. Thus, the active matrix type LCD panel is used as a monitor display for a portable TV or a computer, which is required to quickly display a large quantity of image information.
In these years, with an increase in quantity of information, there is a demand for enhancement of the resolution and display speed of the liquid crystal display panel. As a technique of enhancing the resolution, the number of pixels is increased by miniaturization of the TFT array structure. In this case, an LCD mode, which can provide a response speed of liquid crystal molecules twice to several tens of times higher than the current level, is required to change the alignment of liquid crystal molecules in a period shortened according to the increase in the number of pixels. Such an LCD mode can be selected from Optically Compensated Birefringence (OCB), Vertically Aligned Nematic (VAN), Hybrid Aligned Nematic (HAN), and π-alignment modes using a nematic liquid crystal, and Surface-Stabilized Ferroelectric Liquid Crystal (SSFLC) and Anti-Ferroelectric Liquid Crystal (AFLC) modes using a smectic liquid crystal, for example.
Particular attention has recently been paid to the VAN mode, which has a higher response speed than the conventional twisted nematic (TN) mode and adopts a vertical alignment treatment, thus dispensing with a conventional rubbing process that may cause defects such as electrostatic destruction. Moreover, a design for viewing angle compensation becomes easier when the VAN mode is employed. The viewing angle can be widened by a multi-domain structure that each pixel region of the liquid crystal layer is divided into a plurality of domains between which liquid crystal molecules are set in different tilt directions.
In the above-mentioned multi-domain structure, the plurality of domains are created, for example, by causing an electric field applied from each electrode into the liquid crystal layer to be non-uniform at an inside part or periphery of the electrode, so that the tilt directions can be determined according to the dielectric constant anisotropy of liquid crystal material and the non-uniformity of electric field. Conventionally, sufficient multi-directional components are not obtained in the non-uniform electric field, with a result that the viewing angle characteristic is made uneven. In addition, it is difficult to control the threshold characteristic defining a point from which a change in the transmittance is initiated.